In their highly readable and informative book Cathedral, Forge and Waterwheel, medieval scholars Frances and Joseph Gies recount how Europeans spent much of the 1,000 years between the collapse of the Roman Empire and the Renaissance rebuilding their agrarian civilization. Despite centuries of invasions and disorder, they somehow managed to preserve enough of society’s agricultural base to support the slow emergence of a prosperous civilization.

I thought about the struggles of those farmers as my wife and I prepared and planted our vegetable garden this spring. I thought of their primitive plows as I grabbed my spiffy electric rototiller to churn up our hard clay soil. I reflected on their total dependence on the resources at hand as we drove to the garden supply store to pick up some plastic bags filled with “organic” chicken manure, Chinese-made parts for our drip irrigation system and synthetic-leather work gloves.

Today, we rely on an exceedingly complex system to grow and process our food, whether it is home-grown or store-bought. That system is one of the great unsung achievements of modern civilization: Indeed, it has made modern civilization and our expanding global population possible.

But what if that system begins to break down? How could we feed ourselves if the technological marvel we call industrial agriculture proves unsustainable – if its very success disrupts the climate and depletes the soil and water upon which it depends? How could we garden without our trips to the store? If we had to, could we follow in the footsteps of our ancestors and learn how to survive centuries of disruption?

The breakdown is underway. Most states west of the Mississippi, including California, are blanketed by “severe,” “extreme” or “exceptional” drought, while flooding has disrupted planting in much of the Midwest. “Dirty Thirties” dustbowl conditions have returned to Oklahoma, Texas, Colorado and Kansas. Mountain glaciers and snowpacks are disappearing as massive aquifers are running dry. Topsoil is thinning everywhere, and fertilizer pollution of our waterways is an out-of-control “externality” of industrial farming.

Add these climate and resource problems to the peak of cheap, easy oil production we passed a year or two ago, and we can see that our entire agricultural system is vulnerable to natural and human-made shocks – and perhaps rapid implosion.

What can we do to avert a food crisis? The agricultural system is in the early stages of a downward, accelerating spiral precisely because of the paths it has taken to record productivity and prosperity: overcentralization, vast monocultural enterprises and externalized environmental costs. These trends are likely to grow because they are profitable – albeit in a bubble agro-economy primed to burst.

If the system is to adapt successfully – rather than collapsing and having to be rebuilt as it was during the Middle Ages – it will have to be changed from the periphery. The antidote to centralization and monoculture is to diversify food sources – we need more small to mid-sized farms (pooling their resources as needed), and many more home gardens.

The Victory Garden system, implemented quickly by the British and U.S. governments to alleviate shortages during World Wars I and II, proved that a substantial amount of food – about 40 percent of all vegetables – can be grown in backyards and community gardens. But you don’t have to wait on Washington’s waking up to the developing food crisis to prepare for it at home.

The first step is to save knowledge – human knowledge of appropriate agricultural technology, and nature’s “knowledge” that diversity is the key to adaptation. Compared with our medieval predecessors, our human knowledge base is tremendous. We have records rather than traditions and science rather than folklore, to inform us.

But as we are learning, that knowledge does not necessarily translate into sustainable agricultural practice. And nature’s knowledge – stored in its diverse seeds – is threatened by monocultural practices.

But you can change that system by gathering and sharing knowledge of sustainable food production, growing a wide variety of heirloom vegetables that monocultural corporate farms find unprofitable, conserving water, building soil and learning how to store food without relying completely on your freezer.

We’ll explore these practices in upcoming columns, because sustainable gardening and farming could be a lifesaver at your ecological house.

Philip S. Wenz, who grew up in Durango and Boulder, now lives in Corvallis, Ore., where he teaches and writes about environmental issues. Reach him via e-mail through his website, www.your-ecological-house.com.